The objective of the research is to develop a system of dosimetry for photoradiation therapy, a promising new method of treating malignant tumors by a combination of visible light and a tumor-specific, photodynamically active drug, usually either hematoporphyrin-derivative (HpD) or dihematoporphyrin-ether (DHE). The aims are: to calculate and measure the distribution of the light with depth in the tumor, and relate the absolute space irradiance to the light source (usually laser, power, wavelength, irradiation geometry, and optical properties of the tissue; to measure the concentration of HpD or DHE by fluorimetry and relate the concentration to drug, dosage, time after injection, and light exposure (potential reduction in concentration because of photodecomposition); to determine the relative photodynamic effectiveness as a function of wavelength and oxygenation; to develop a method of monitoring dose rate in vivo by using fluorescence as a measure of absorption rate and correcting for diffusion of the light and relative photodynamic effectiveness; and to confirm the validity of the dosimetry methods by predicting and measuring biological response from the effective absorbed dose as defined.